1. Field of the Invention
The present invention relates to a display apparatus that includes electroluminescence (hereinafter referred to as EL) elements and thin film transistors (hereinafter referred to as TFTs) which are fabricated on a substrate, and also to a method of fabricating the same.
2. Description of the Related Art
Recently, display apparatus using TFT elements and EL elements such as organic EL elements have been noted as display devices, in place of the CRTs (Cathode Ray Tubes) or LCD (Liquid Crystal Display) apparatus.
FIG. 1 is a cross sectional view illustrating a conventional display apparatus including organic EL elements and TFT elements. FIG. 1 shows a laminated structure in which an organic EL element is deposited over a TFT structure. The structure is formed as follows:
A gate electrode 2 is formed on a transparent insulating substrate 1 such as glass or synthetic resin. An insulating film 3 is formed on the gate electrode 2. An active layer 4 of polycrystalline silicon is formed on the insulating film 3. A source region 4s and a drain region 4d into which impurities are implanted are formed in the active layer 4. An interlayer insulating film 8 formed of a SiO2 film 6 and a SiN film 7 is formed on the active layer 4. The source region 11s is connected to the source electrode 10s via the contact hole 9 formed in the interlayer insulating film 8. The drain region 4d is connected to the drain electrode 10d via the contact hole 9 formed in the interlayer insulating film 8.
Planarization insulating film 11 is formed on the electrodes 10s and 10d and the interlayer insulating film 8. The source electrode 10s is connected to an anode electrode 28 of an organic EL element formed on a TFT element via the contact hole 12 formed in the planarization insulating film 11.
The organic EL element is formed by successively laminating an anode 2 formed of: a transparent electrode of ITO (Indium Tin oxide); an organic layer comprised a second hole transfer layer 27 of MTDATA (4,4′-bis(3-methylphenylphenylamino)biphenyl), a first hole transfer layer 26 of TPD (4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine), a luminous layer 25 of Bebq2(10-benzo[h]quinolinol-beryllium complex) containing Quinacridone derivative, and an electron transfer layer 24 of Bebq2; and a cathode electrode 23 of magnesium and indium alloy (MgIn). The organic layer is made of an organic chemical compound. Thus, an EL element is constructed the organic layer, the anode electrode 28, and the cathode electrode 23.
In the organic EL element, the holes injected from the anode electrode 28 and the electrons injected from the cathode electrode 23 are recombined inside the luminous layer 25. Excitons are generated by exciting the organic molecules of the luminous layer 25. The luminous layer 25 radiates light through the process of the excitons disappearing. The light is radiated out from the transparent anode electrode 28 through the transparent insulating substrate 1.
However, in the conventional display apparatus structure, since the organic EL element emits light through the side of the substrate 1 on which TFT elements are formed, the TFT structure blocks the emitted light so that the display pixel aperture ratio cannot be increased.
Furthermore, since the TFT elements must be small-sized to the extent that the luminous light is not blocked, there are severe limitations on increasing the size of each TFT element as well as the TFT element capability.